In addition to a central processing unit (CPU) and a memory, a computer also requires interfaces to the outside for its operation that can be constructed in different ways. A system bus is directly connected to the computer, which is generally constructed as a parallel interface so that depending on the processor clock, or on the bus clock, a multitude of bits can be allowed in and out. If information is to be transferred via lines, this can generally also occur via parallel interfaces, whereby the line length is limited due to the large amount of lines required. Transfer processes were therefore developed for the distance transfer of information or data, in which the initially parallel existing signals were converted into serial signal so that they could then be sent and received via a low amount of lines. For this purpose, computers are usually equipped with network cards that are connected to the respective system bus, whereby standard parallel interfaces were recommended in this case. One example of such a standard interface is the so-called PCI bus. A network controller or a network card is successively connected to such a bus, which in addition to the network controller also contains an additional interface that is adjusted to the selected transfer medium, or to the selected network structure. Among other tasks, this media-specific interface takes on the adjustment of the levels to the post-connected line network, whereby bus networks are commonly used. In the case of bus networks, all computers are connected to a mutual bus, whereby each participant can access the bus, and can reach each participant connected. In order to control access to such bus structures, the CSMA (carrier sense multiple access) process is used, for example. In this process, an attempt is made to avoid collisions by simultaneously occurring transfers. If two participants simultaneously recognized and sent a free line network, such collisions would occur. However, this is prevented by the fact that the transfer media is tapped by the stations before the transfer is started, for which bit structures are used with which collision recognition is possible. Such bit structures are called CSMAICD packets, whereby CD stands for “collision detection” or collision recognition. In addition to bus networks, star networks, ring networks, and token ring networks are common, and various types of transfer protocols are used with which a more or less large maximum transfer speed can be achieved. Such transfer protocols have been known, for instance, as Ethernet protocols (IEEE 803), or as firewire protocols (IEEE1394). The analog applies to, for instance, CAN, FDDI, ATM, or gigabit Ethernet protocols.
The network controller, together with the media-specific interface, provides the translation of the parallel data flows into a serial data flow, whereby the desired conventions, or protocols are maintained in order to avoid any collisions. Network cards usually contain memory in order to retain information as long as a data line is occupied, or the data packet is incomplete, or is present in a form that is unsuitable for the protocol. This stored information is subsequently fed into the network when a free line is detected. Because of this intermediate storage until the release of transfer, the data packets experience various delays due to the network card. This is also true for so-called switches, in which certain information to be sent to an addressee is stored up until a certain time, at which a larger packet can be sent at a higher speed.
In computer networks that must be checked to ensure that a universal time base is available to all computers, it is also important to recognize when the information was received from another networked computer in addition to when the information was sent. Although computer clocks for the clocking of a computer allow for the determination of time at which a processor has made information available to the network card, they do not recognize when the network card has actually performed the transfer via the data transfer line. Therefore, additional computer clocks have been recommended, by means of which the time critical data packets are equipped with a time stamp at the time of the actual transfer. Such computer clocks have already been connected between the network controller and the media-specific interface, whereby the network controller and the media-specific interface are connected to each other via a media-independent interface (MIIF), and the computer clock is connected between these two components. In order to make complete information on the actual time of transfer of the information available to the respective sending CPU, this inter-connected computer clock must echo the time of the actual transfer to the assigned processor. In this regard, it is advisable to perform an echo into the system bus via a separate component group, whereby such components can be called PCI bridges, for instance, and communicate with the PCI bus of the computer. The circuit complexity and hardware expenditure of such modifications, however, is relatively high and requires the additional equipment of computers with additional interfaces and additional interface cards.